Because an IPv6 (Internet Protocol Version 6) wireless sensor network has a limited computing capability and communications capability, the ROLL (Routing Over Low Power and Lossy Networks) working group of the IETF (Internet Engineering Task Force) has proposed, in RFC6550, an RPL (IPv6 Routing Protocol for Low-Power and Lossy Networks) routing mechanism that is applicable to the IPv6 wireless sensor network. However, this RPL routing mechanism is designed for a static IPv6 wireless sensor network, which cannot meet a requirement of the IPv6 wireless sensor network in a mobile scenario.
To ensure correct execution of the RPL routing mechanism in the mobile scenario, a problem of node mobility in the IPv6 wireless sensor network needs to be resolved. A document entitled Mobility Enhanced RPL For Wireless Sensor Network mentions that a dynamic DIS (Destination Oriented Directed Acyclic Graph Information Solicitation) management mechanism is designed to determine the problem of node mobility in the IPv6 wireless sensor network.
Specifically, in the dynamic DIS management mechanism, a sending period for sending a DIS message by a node is changed, and then a sending period for sending a DIO (Destination Oriented Directed Acyclic Graph Information Object) message as a reply by a neighboring node of the node is changed, so that a mobile node in the IPv6 wireless sensor network can update acyclic graph information in a timely manner according to an actual network status, so as to maintain a connection between the mobile node and a network topology.
When a node in the IPv6 wireless sensor network moves, a Rank value (that is, a value of a quantity of hops from the node to a convergence node of the IPv6 wireless sensor network, where the quantity of hops is counted as follows: one hop is counted if a node can directly communicate with another node instead of communicating with the another node through another node), an alternate parent node set, and a preferred parent node change. Therefore, a change of the preferred parent node of the node is directly used as an indication for determining that the node moves in the IPv6 wireless sensor network. That is, it is determined that a node moves as long as a preferred parent node of the node changes.
FIG. 1 is a schematic structural diagram of a network topology of an IPv6 wireless sensor network.
It can be seen from FIG. 1 that, a parent node A is connected to three child nodes: B1, B2 and B3; the node B1 is connected to two child nodes: C1 and C2; the node B2 is connected to one child node C3; B3 is connected to two child nodes: C4 and C5; the node C1 is connected to one child node D1; the node C2 is connected to one child node D2; the node C3 is connected to one child node D3; the node C4 is connected to one child node D4; C5 is connected to one child node D5. It is assumed that D5 is a movable node, a current preferred parent node of the node D5 is C5, and an alternate parent node set is {A, B1, B2, B3, C1, C2, C3, C4, D1, D2, D3 and D4}. According to the DIS management mechanism, when the preferred parent node C5 of the node D5 changes, it is determined that the node D5 moves. However, when the node C5 in the IPv6 wireless sensor network fails (or cannot work), to ensure connectivity of nodes in the network topology, the node D5 needs to choose a new preferred parent node, which means that the preferred parent node of the node D5 changes, but the node D5 may not move in this case. That is, a change of a preferred parent node cannot indicate that a node moves. In other words, it is quite inaccurate to determine that a node moves simply based on a change of a preferred parent node of the node.
In conclusion, a method for determining a node movement is in urgent need, to resolve a problem of low accuracy in determining a node movement in the prior art.